On December 1, 2015 the Subcommittee on Strategic Forces of the U.S. House Armed Services Committee held a hearing on "Russian Arms Control Cheating: Violation of the INF Treaty and the Administration's Responses One Year Later". Rose Gottemoeller and Brian McKeon were invited to testify, just as they were a year ago. There was nothing particularly new there, at least not in the open session, but a few details are worth mentioning.
First, the administration line on discovering the suspect cruise missile has finally taken its final shape - although it is still believed that the tests began in 2008, "it was the end of 2011 when [the United States] had indications that this missile was a missile of concern" (see the exchange after 1:13:52 in the video). Before that, the line goes, the United States didn't even had suspicions about the violation.
As I understand what Rose Gottemoeller said, before that time the missile was tested in treaty-compliant manner, either from a fixed launcher or from sea (or maybe from an aircraft). Which definitely makes sense if this is essentially the same missile. (In all likelihood, this is the missile that was used against Syria in October - Kalibr-NK.) Then, in 2011, Russia probably tested it from a mobile launcher, which immediately made it non-compliant with the treaty.
Rose was very specific about my SLCM/technicality theory being wrong - "We've made it very clear [to the Russians] that this is not a technicality or a one-off event, or a case of mistaken identity. Again, [there was] a notion of this being a sea-launched cruise missile..." (it's at 15:58).
I am not sure I fully buy these arguments, though. On the end of 2011 claim, it is clear that the administration is under considerable pressure from Congress - there is no way they could admit that anyone had an inkling of a violation in 2010, at the time the New START was being ratified. My guess is that someone somewhere in the U.S. intelligence community may have had suspicions, although they probably had not been reported up the chain of command.
On the technicality theory, it is, of course, possible that I got it wrong and there is indeed a dedicated launcher that has been used to launch the new missile. But at the same time, we don't really expect the administration to say it was indeed a technicality - definitely not today, when the issue got that much attention. Even if there is no dedicated launcher, the administration will definitely stick to its line, especially since strictly speaking it is correct - as far as the INF Treaty is concerned, it is not an SLCM. On a larger point, however, judging from what was said yesterday, I am probably correct - the missile in question appears to be virtually identical to a SLCM (Kalibr-NK?), but it's just launched from a mobile launcher.